Fix regex in build_gdk_image script

Ref: https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/20782

scripts/build_gdk_image

@@ -7,7 +7,7 @@ source "$(dirname "$0")/utils.sh"
 REGISTRY="${CI_REGISTRY}/${CI_PROJECT_PATH}"
 SHA_TAG="${CI_COMMIT_SHA}"
 BRANCH_TAG="${CI_COMMIT_REF_SLUG}"
-STABLE_BRANCH_PATTERN="^[\d-]+-stable-ee$"
+STABLE_BRANCH_PATTERN="^[0-9-]+-stable-ee$"
 
 IMAGE="${REGISTRY}/gitlab-qa-gdk"